Restore 1 hit point per day. Simple, easy to follow, makes healing take a nice long time. Only issue is that Fighters take longer to heal then classes with less HP. Giving them say 2 a day or 1d4 a day might work a little better, but ruins some of the ease.
Easy Seasons- Restore to full hit point between sessions. Not really a healing method. Abstracted 3 month period of time gives enough time for theoretically any injury or damage a character has to heal, but gives little useful information if you need current HP between seasons.
Slow Seasons- Restore maximum possible roll of class HD + Constitution per season. Not the modifier, the whole stat. Might put too much emphasis on stats though.
Heroic- Roll your class HD and restore that much, each day. You'll essentially heal in about your level's worth of days, which means there is no longer weeks and months long healing.
Slow- Restore 1 class HD of hit points per week healed. High level characters still take longer to heal, but characters heal a bit slower on average. Fighters can heal faster then the Traditional slow method, but things are more random. If taking the maximum HD possible roll of the class instead as healing per week, still a bit slower unless if you're a d8 or higher class. If you're interrupted halfway through a week you spent healing, either don't get any health or average out half or a third of the roll or whatever.
Boring Fast- Restore 10% hit points per day. You'll be fully healed in 10 days no matter what using this method. If you use 10% of your current hit points, then you start healing slow but heal faster later on. OSR characters rarely get enough hit points for this to matter as much.
Boring Slow- Heal 10% hit points per week. Maybe add Con bonus to amount healed per week, which would speed or slow things down considerably. Characters with low health and low Con may not ever get better; minimum of 1 hit point per week?
Needlessly Complicated- Roll Class HD. If you get a 4 or higher, heal 1 hit point for that day. If you get a 6 or higher, heal 1 hit point and restore the most damaged ability score by 1 point. If you don't have any damaged stats- heal 2 hit points instead. This method could mean classes with very small HD may never recover from their damaged attributes- d4 Wizards get a bad cough and keep it forever without magical healing or a doctor because of their sickly lifestyle.
Slow & Complicated- As above, but only roll twice per week. Could take months to heal. Want to make it even slower? Only restore a damaged attribute if all hit points are full, thus meaning you only restoring a minimum number of points. Maybe attributes heal whenever they are rolled instead, so hit points and attributes come back somewhat randomly and slowly.
Flesh & Grit- This one is easy; restore all Grit per day, or even per a long rest? Pick a slower method for flesh, or 1 hit point per day of flesh? Not sure what's all been written about this one.
Just Dumb- Heal 1 hit point per day per 10,000c worth of property, items, and servants you you have. Takes ages to heal if you're poor.